What is the role of cardiac MRI in diagnosing and treating myocarditis?

Role of Cardiac MRI in Diagnosing and Treating Myocarditis

Cardiac MRI is the non-invasive test of choice for diagnosing myocarditis, with high diagnostic accuracy that can detect specific tissue changes associated with myocardial inflammation, guide treatment decisions, and provide prognostic information. 1

Diagnostic Value of Cardiac MRI

• Cardiac MRI can differentiate ischemic from nonischemic cardiomyopathy by the pattern of myocardial damage on post-gadolinium contrast sequences, with myocarditis typically showing epicardial or midwall enhancement patterns rather than the endocardial pattern seen in ischemic disease 1

• The updated Lake Louise Criteria for diagnosing myocarditis requires at least one T2-based criterion (indicating edema) and at least one T1-based criterion (indicating hyperemia, increased extracellular volume, or fibrosis) for high specificity diagnosis 1

• Cardiac MRI can detect three key pathophysiological features of myocarditis:

  • Myocardial edema (using T2-weighted imaging or T2 mapping)
  • Hyperemia/capillary leak (using early gadolinium enhancement)
  • Irreversible myocardial injury/fibrosis (using late gadolinium enhancement) 1

• T1 and T2 mapping techniques have improved the diagnostic accuracy for myocarditis compared to conventional sequences, with native T1-mapping showing sensitivity of 90%, specificity of 91%, and accuracy of 91% 1

Clinical Impact and Treatment Guidance

• Cardiac MRI has been shown to impact clinical decision-making in >50% of patients with suspected myocarditis and provides a new diagnosis in 11% of patients 1

• The presence of late gadolinium enhancement in biopsy-proven viral myocarditis may predict subsequent risk of ventricular arrhythmias and cardiovascular death, providing important prognostic information 1

• Cardiac MRI can help localize inflammatory changes to reduce sampling errors when endomyocardial biopsy (EMB) is indicated, improving therapeutic decision making and prognostication 1

• The pattern of myocardial inflammation evolves from focal to diffuse during the first 2 weeks after symptom onset, which can be visualized by contrast-enhanced MRI 2

Limitations and Considerations

• Cardiac MRI has lower sensitivity for diagnosing chronic myocarditis (>14 days from symptom onset), with diagnostic accuracy dropping from 81% in acute cases to 45% in chronic cases 1

• While the Lake Louise Criteria have a diagnostic accuracy of approximately 80% to rule in myocarditis, the negative predictive value is less than 70%, meaning a negative MRI cannot completely exclude myocarditis 3

• T2 mapping may be more specific for acute inflammation compared to T1 mapping, which is also sensitive to water detection in more chronic settings such as scarring or other causes of expanded extracellular space 1

• Different viral etiologies may show different late gadolinium enhancement patterns, potentially helping identify the causative agent 1

Integration with Other Diagnostic Methods

• Cardiac MRI should be performed in patients with symptoms of myocarditis, evidence of myocardial injury, and suspected viral etiology after excluding coronary artery disease 1, 4

• The American College of Cardiology recommends cardiac MRI for hemodynamically stable patients with suspected myocardial involvement 4

• While endomyocardial biopsy remains the gold standard for confirming myocarditis, cardiac MRI is recommended as a Class I investigation to identify myocarditis in patients with suspected or established heart failure 1

• The European Society of Cardiology considers myocarditis clinically suspected if ≥1 clinical presentation and ≥1 diagnostic criteria from different categories are present, with cardiac MRI being one of the key diagnostic tools 1

Emerging Techniques

• Novel cardiac MRI techniques, especially T1 and T2 mapping, provide tissue characterization regarding inflammation without reliance on reference tissue, overcoming limitations of the traditional Lake Louise Criteria 3, 5

• Contrast enhancement steady-state free precession (ceSSFP) technique has been proposed as a fast and effective method to assess myocardial hyperemia in acute myocarditis 6